The present invention relates to an apparatus for controlling a clutch using an electric motor and a torque-to-thrust mechanism.
Automatic transmissions have long been used in vehicles as a convenient substitute for manual transmissions. Today automatic transmissions are by far the most popular option for the majority of the driving public. Having an automatic transmission in a vehicle eliminates the need for a driver to master the skilled operation of manual gear shifting. Elimination of this operation, though beneficial in some respects, does come at a cost: decreased vehicle efficiency.
One of the inefficiencies of an automatic transmission is the high-pressure pump. The high-pressure pump produces the transmission fluid (oil) pressure, and thereby serves a number of important roles. First, the high oil pressure is required to maintain torque converter charge pressure, which is the torque converter oil inlet pressure at the centerline of the transmission. It is necessary to maintain this pressure to avoid cavitation, which is not only inefficient, but can be damaging. The high-pressure pump also supplies the fluid pressure necessary to selectively apply the clutches that provide the desired gear ratios. The control of the clutches also requires a complex system of solenoids, valves, shaft seals, centrifugal clutch balance, and oil routing to ensure that oil at the proper pressure is received by each clutch when it is applied, and that the oil is properly exhausted when each clutch is released.
Accordingly, it is desirable to provide an apparatus for engaging the clutches in an automatic transmission that eliminates the need for the high-pressure pump, the solenoids and the valve body, thereby increasing the vehicle efficiency and decreasing its mass and size, while still maintaining the benefits associated with having an automatic transmission.
The present invention provides an apparatus for applying clutches in an automatic transmission that eliminates the need for a high-pressure pump, solenoids, and a valve body. The transmission fluid is normally pressurized by the pump and controlled by solenoids and valves in the valve body. The solenoids regulate and direct the flow of the fluid through the valves, thereby controlling pistons that apply clutches. In the present invention, this system is replaced by a series of electric motors and torque-to-thrust mechanisms which work together to control the clutches. The motors are conveniently mounted on the bottom of the transmission and have motor shafts that enter the transmission through the transmission housing. A driving element such as a worm gear, spur gear or bevel gear is attached to each motor shaft, and drives a torque-to-thrust mechanism. The choice of the drive element is primarily dictated by the required speed ratios between the motor and the torque-to-thrust mechanism, and by the motor shaft orientation which is optimized for packaging. The driving element attached to each motor shaft causes rotation of a drive wheel in the torque-to-thrust mechanism. It is worth noting that the driving element can also be a sprocket, in which case a chain connects the sprocket with the drive wheel. The center of the drive wheel is located on the center line of the transmission, and it is piloted on the transmission case by a bushing or bearing as it rotates around the transmission center line.
There are many potential torque-to-thrust mechanisms that can be used to perform the role of transforming the motor torque into a linear thrust force. In one version, one end of a coil spring is affixed to the drive wheel such that rotation of the drive wheel causes rotation of the spring. The coils of the spring are fed through a small aperture in an apply ring, such that at least a portion of the coils are disposed on each side of the apply ring. The apply ring is rotationally constrained by splines in the transmission housing. As the drive wheel and spring rotate, the spring wire is transferred from one side of the apply ring to the other, resulting in the number of coils on one side of the apply ring decreasing. This causes the apply ring to move linearly in the direction of the decreasing coils. Continued rotation of the drive wheel and coil spring in this direction causes the apply ring to contact an apply plate. At this point, the torque on the drive wheel increases, which results in a thrust load on the apply plate and the subsequent application of the clutch. Rotation of the drive wheel and the coil spring in the opposite direction moves the apply ring away from the apply plate, thereby disengaging the clutch.
There are several methods by which the application of the clutch is controlled. Primary among these are control of the motor torque and control of the apply plate position. In the latter example, a position spring is used to convert position into a thrust. Because the deflection of the spring is related to the position of the apply plate, the thrust, or clamp load, is easily determined through measurement of the motor rotation. Utilizing torque control to ensure smooth application of the clutch requires control of the torque of the drive motor, since this in turn controls the thrust of the apply ring to the apply plate. To accomplish this motor control, an ammeter is used to monitor the current load on the drive motor, and an encoder is used to measure the motor""s rotational position.
When the apply ring is not contacting the apply plate, there is very little motor torque and the motor is rotated utilizing any of the well known motor speed control systems. As the apply ring exerts a force on the apply plate, the motor torque increases, the ammeter detects an increase in the current load, and the motor is then rotated utilizing any of the well known motor torque control systems. The processor used to control the various elements within the transmission, including the present invention, is a transmission control module. Although transmission control modules are currently used in automatic transmissions, they have a relatively low current draw because their primary function is to control the solenoids in the valve body. The transmission control module utilized in the present invention is a modification of the standard module in that it is designed to handle a higher current load necessitated by its new function: operating the electric drive motors.
Another spring may be included in the torque-to-thrust mechanism to increase the mechanism""s compliance such that the transmission control module can control the drive motor with the requisite level of sensitivity. A separate motor is used for each clutch, even in a six speed transmission. In addition to these drive motors, an extra motor can be mounted on the bottom of the transmission housing to pump a small volume of low pressure fluid through the transmission, thereby cooling and lubricating the moving components.
Accordingly, one aspect of the present invention provides an apparatus for controlling the clutches in an automatic transmission on a vehicle that allows for elimination of the valve body and its associated components.
A further aspect of the invention provides an apparatus for controlling the clutches in an automatic transmission on a vehicle that allows for elimination of the high-pressure pump.
Another aspect of the present invention provides an apparatus for controlling a clutch in an automatic transmission on a vehicle. The apparatus comprises an electric motor affixed to a housing of the transmission, and having a motor shaft with a driving element rotatably attached to it. The apparatus further comprises a torque-to-thrust mechanism driven by the driving element and includes a thrust element for imparting a linear force to apply the clutch. The apparatus also includes a sensing system configured to output at least one electronic signal related to the magnitude of the linear force, and a transmission control module that receives the at least one electronic signal from the sensing system and controls the electric motor.
It is another aspect of the present invention to provide an apparatus for controlling clutches in an automatic transmission on a vehicle. The apparatus comprises a plurality of electric motors fixedly attached to a housing of the transmission, each motor having a motor shaft with a driving element rotatably attached to it. The apparatus further comprises a plurality of torque-to-thrust mechanisms, each driven by a corresponding driving element, and each including a thrust element for imparting a linear force to a corresponding clutch. The apparatus also includes a plurality of sensing systems, each configured to output at least one electronic signal that is related to the magnitude of the linear force on a corresponding clutch. A transmission control module receives the electronic signals from the sensing systems and controls the electric motors.
Yet another aspect of the present invention provides a vehicle having an automatic transmission including an apparatus for controlling at least some of the clutches in the transmission, thereby reducing both the vehicle space required by the transmission and the power consumed by the transmission. The apparatus comprises a plurality of electric motors fixedly attached to a housing of the transmission, each motor having a motor shaft with a driving element rotatably attached to it. The apparatus further comprises a plurality of torque-to-thrust mechanisms, each driven by a corresponding driving element, and each including a thrust element for imparting a linear force to a corresponding clutch. The apparatus also includes a plurality of sensing systems, each configured to output at least one electronic signal that is related to the magnitude of the linear force on a corresponding clutch. A transmission control module receives the electronic signals from the sensing systems and controls the electric motors.